plugins: add Plugins section to Chat Customizations

[connor4312]

Add a new Plugins sidebar section to the AI Customization Management editor and sessions customizations view.

• Add Plugins to AICustomizationManagementSection enum (core and sessions)
• Create PluginListWidget following the MCP list widget pattern:
  • Groups installed plugins into Enabled/Disabled collapsible sections
  • Browse Marketplace toggle with search
  • Install buttons for marketplace plugins via IPluginInstallService
  • Context menu with Enable/Disable/Open Folder/Uninstall actions
• Wire plugin list widget into management editor with embedded detail view using AgentPluginEditor
• Add Plugins section to sessions air customization overview and shortcuts widget
• Track plugin count with IAgentPluginService in total customization count badge
• Reuse MCP list widget CSS patterns for consistent UI

Cc @joshspicer

(Commit message generated by Copilot)

[Copilot]

Pull request overview

Adds a new Plugins section to the Chat/AI Customizations management surfaces (workbench editor + sessions UI) and introduces a dedicated plugin list widget with marketplace browsing and an embedded details editor.

Changes:

• Adds Plugins to AICustomizationManagementSection and wires it into the workbench AI Customization Management editor.
• Introduces PluginListWidget (installed + marketplace browse) and embeds AgentPluginEditor as a details view.
• Updates Agent Sessions UI (overview + toolbar + counts + workspace filtering) to include plugin-related sections and counts.

Reviewed changes

Copilot reviewed 10 out of 10 changed files in this pull request and generated 3 comments.

Show a summary per file

File	Description
src/vs/workbench/contrib/chat/common/aiCustomizationWorkspaceService.ts	Adds Plugins to the shared management section enum.
src/vs/workbench/contrib/chat/browser/aiCustomization/pluginListWidget.ts	New list widget for installed/marketplace plugins, grouping, search, install, and context menu actions.
src/vs/workbench/contrib/chat/browser/aiCustomization/media/aiCustomizationManagement.css	Adds containers/styles for plugins list + embedded plugin detail editor.
src/vs/workbench/contrib/chat/browser/aiCustomization/aiCustomizationWorkspaceService.ts	Exposes the Plugins section in workbench management sections.
src/vs/workbench/contrib/chat/browser/aiCustomization/aiCustomizationManagementEditor.ts	Integrates Plugins section, list widget, and embedded AgentPluginEditor detail view.
src/vs/sessions/contrib/sessions/browser/customizationsToolbar.contribution.ts	Adds Plugins shortcut entry and reactive plugin count badge.
src/vs/sessions/contrib/sessions/browser/customizationCounts.ts	Includes plugin count in total customization count (optional service param).
src/vs/sessions/contrib/sessions/browser/aiCustomizationShortcutsWidget.ts	Passes plugin service to total count calculation.
src/vs/sessions/contrib/chat/browser/aiCustomizationWorkspaceService.ts	Includes plugin storage in filters and adds Plugins section in sessions workspace service.
src/vs/sessions/contrib/aiCustomizationTreeView/browser/aiCustomizationOverviewView.ts	Adds Plugins to overview list and updates count reactively.

---

You can also share your feedback on Copilot code review. Take the survey.